From the German publication "Deutsche Hebe- und Fordertechnik", No. 2/73 of February, 1973, pages 90 and 92, an attachment of this type is known which comprises two juxtaposed vertical support plates carrying respective pairs of prongs, these plates being secured to the front face of a vertical lifting plate of a fork-lift truck for joint raising and lowering along with any load engaged thereby. That assembly is somewhat unwieldy since, on the one hand, the lifting plate must be wide enough to hold the two support plates and, on the other hand, the mechanism required for a lateral shifting of the prongs--to accommodate single or double pallets--is quite complex.
An improved attachment of this character is disclosed in Austrian Pat. No. 342,500 and comprises a common support plate for the two outer and the two inner prongs. The outer prongs are linked with the support plate by a pair of fluidic jacks enabling their relative lateral displacement. The inner prongs can be entrained by the outer prongs over part of their travel, by couplers not particularly described, or can be loaded by compression springs tending to separate them when the outer prongs are moved farther apart. The support plate has a width only slightly less than the maximum separation of the outer prongs, the difference resulting from a generally Z-shaped horizontal profile of the upright legs of the outer prongs forming rabbets which accommodate the upright legs of the adjoining inner prongs in a contracted position in which all four prongs are closely grouped for engagement with a single pallet.